Download Section 3.3 Day 1

Tuesday, Oct. 29th: “A” Day
Wednesday, Oct. 31st: “B” Day
 Homework questions?
 Sec. 3.2 Quiz: “Structure of Atoms”
 Begin Section 3.3: “Electron Configuration”
 Atomic models
Rutherford, Bohr, quantum, orbitals
 Electrons and light
Electromagnetic spectrum,
line-emission spectrum, ground state, excited state
 Homework:
“Isotopes” worksheet
“Atomic Number/Mass Number” worksheet
Homework Questions
“Writing Nuclear Symbols” Worksheet
Sec. 3.2 review, pg. 89: #1-8
Quiz
Section 3.2: “Structure of Atoms”
You can use your notes, your book and your
1:00 partner to complete this quiz…
Hints:
#2: be careful of the word “only”.
What do you know for sure about
the rays produced by the cathode
ray tube?
#8: the word “total” in b) means
protons + electrons + neutrons
Use the process of elimination to help choose the correct
answers!
Rutherford’s Model Proposed Electron Orbits
Rutherford’s findings led to the replacement
of Thomson’s plum pudding model with a
nuclear model of the atom.
Rutherford suggested that electrons are like
planets orbiting the sun and revolve around
the nucleus in circular or elliptical orbits.
Because Rutherford’s model could not explain
why electrons did not crash into the nucleus, it
was replaced only two years later by a model
developed by Niels Bohr.
Bohr’s Model Confines Electrons to Energy Levels
In Bohr’s model, electrons can only be certain
distances from the nucleus. Each distance
corresponds to a certain quantity of energy that an
electron can have.
An electron that is as close to the nucleus as it
can be is in its lowest energy level.
The farther an electron is from the nucleus, the
higher the energy level that the electron
occupies.
The difference in energy between two energy
levels is known as a quantum of energy.
Think of Bohr’s energy levels as rungs on a
ladder, with Earth being the nucleus…
You can only be on certain energy levels, or rungs,
of the ladder but you can’t be in between them.
You are at your lowest energy level at the bottom
of the ladder. (closest to Earth)
You are at your highest energy level
at the top rung of the ladder.
An electron can only be in certain,
definite energy levels, not in between
them.
Atomic Models
Rutherford
Electrons orbit the nucleus
just as planets orbit the sun
Bohr
Electrons travel around
the nucleus in specific
energy levels
Electrons Act Like Both Particles and Waves
In 1924, Louis de Broglie suggested that electrons
behaved like waves that are confined to the space
around a nucleus.
As waves, electrons could have only certain
frequencies which correspond to the specific
energy levels where electrons are found.
Quantum Model (electron cloud model)
**the present-day model of the atom**
In this model, electrons are located in orbitals.
Orbital: a region in an atom where there is a high
probability of finding electrons.
Orbitals are sometimes called electron clouds
because they do not have sharp boundaries.
Because electrons can be in other places, the
orbital has a fuzzy boundary like a cloud.
A single orbital can hold a maximum of 2
electrons.
Electromagnetic Spectrum: all of the
frequencies or wavelengths of electromagnetic
radiation.
Our eyes are sensitive
to only a small portion of
the electromagnetic
spectrum.
Hydrogen’s Line-Emission Spectrum
Light Emission
When a high-voltage current is passed through a
tube of hydrogen gas at low pressure, lavendercolored light is seen. When this light passes through
a prism, you can see that the light is made of only a
few colors. This spectrum of a few colors is called a
line-emission spectrum.
Experiments with other gaseous elements show
that each element has a unique line-emission
spectrum that is made of a different pattern of
colors.
It’s like a “fingerprint” for each element.
Light Emission
In 1913, Bohr showed that hydrogen’s
line-emission spectrum could be explained by
assuming that the hydrogen atom’s electron can
be in any one of a number of distinct energy
levels.
An electron can move from a low energy level to a
higher energy level by absorbing energy.
Electrons at a higher energy level are unstable
and can move to a lower energy level by releasing
energy. This energy is released as light that has a
specific wavelength.
Each move from a particular energy level to a
lower energy level will release light of a different
wavelength.
Light Provides Information About Electrons
Ground state: the lowest energy state of a
quantized system. (bottom rung of ladder)
If an electron gains energy, it moves to an excited
state.
Excited state: a state in which an atom has
more energy than it does at its ground state.
Light Provides Information About Electrons
An electron in an excited state will release a
specific quantity of energy as it quickly “falls”
back to its ground state and it emits a
characteristic wavelength of light.
This energy is emitted as certain wavelengths
of light, which give each element a unique,
line-emission spectrum.
Homework (2 worksheets)
“Isotopes”
“Atomic Number/Mass Number”
I know we covered a LOT of background
material today to get ready to write electron
configurations next time…
So, these worksheets should be a
little more concrete and, hopefully,
easier to understand.
Remember to update your KWL as we go
through this chapter…
Happy Halloween!!